1. Field of the Invention
The present invention relates to a system and a method for synchronous optical network (SONET) network service access point (NSAP) addressing.
2. Background Art
Conventional synchronous optical network (SONET) equipment uses two types of addresses to communicate with respective neighbors (i.e., respective network elements in an assigned area), a Transport Identifier (TID) and a Network Service Access Point (NSAP). The TID is a user-friendly name (40 character string) that is assigned to each respective network element (NE), similar to a domain name server (DNS) name. A TID has no inherent uniqueness or hierarchy. The NSAP is a 20 Byte field, broken down into categories as defined in ISO/IEC 8348:2002(E).
Referring to FIG. 1, a diagram 10 illustrating the categories of an NSAP is shown. The NSAP 10 includes of two distinct portions, an Initial Domain Portion or Part (IDP) 20, and a Domain Specific Portion (DSP) 30. The IDP 20 is a three Byte field that includes an Authority and Format Identifier (AFI) and an Initial Domain Identifier (IDI).
The AFI identifies the IDI format and the DSP syntax. For SONET, the value of the AFI is 39 (decimal), which identifies the ISO DCC (Data Country Code) as the address format and preferred binary encoding for the DSP 30. The ISO DCC is a three-digit numeric code allocated according to ISO 3166. The IDI portion of the IDP 20 has the value of 840 (decimal) for the United States. The IDI Pad portion of the IDP 20 is required to make the IDI an integral number of bytes, and is always equal to 1111 (decimal).
Referring to FIG. 2, a diagram illustrating an alternative description of the NSAP 10 is shown. Example values of the octets and definitions for respective fields are shown.
The NSAP address is a larger address than the TID, and the NSAP address confers hierarchy and global uniqueness to each NE, similar to an Internet protocol (IP) address and a media access control (MAC) address. An NSAP is used to securely route management traffic through a respective network. An NSAP includes two parts, the area part and an equipment specific part. One example of conventional equipment includes a default area address. The default area address is not changed when the equipment is placed into service. The equipment specific part includes a unique MAC address. As a result, all of the equipment that is connected is implemented in a single area, and a single area can only operate with up to a maximum of 150 addresses. As such, a 151st element cannot be managed in a single area. As additional equipment is installed, the deficiency caused by the limit of 150 MAC addresses in a single area is increasingly more frequently encountered.
Target Identifier Address Resolution Protocol (TARP) is used to correlate between the two types of addresses. For example, when a network is implemented having two NEs with respective TIDs (e.g., NE1 and NE2), the TID for NE2 is known to NE1. However, the NSAP for NE2 is not known to NE1. When a communication is to be performed between NE1 with NE2, NE1 broadcasts a TARP request to obtain the NSAP for NE2. When the NE2 receives the TARP request, the NE2 returns a message to the NE1 including the NSAP and the TID for NE2. The NE1 can subsequently communicate directly with the NE2.
One conventional approach used on the SONET Data Country Code (SDCC) overhead has a basic address limitation of 50 addresses by definition. The limit has been extended to 150 addresses by many but not all SONET equipment vendors. The limit restricts the number of network elements that can be connected in a level one routing area. The lowest address restriction on a network element type determines the maximum number of addresses for a routing area. In the conventional approaches where the limit remains at 50 addresses, the limit restriction reduces to 50 the routing areas addresses for all elements in the respective routing area.
In another conventional approach, the address restrictions have been accommodated by keeping routing areas physically small. The routing areas are kept physically small by limiting the number of rings that are controlled by an operations controller, turning off unneeded SDCC channels, and avoiding unnecessary C-net connections. However, keeping routing areas physically small requires considerable effort reconfiguring the management network. As the number of DCC channels on a network element have increased, keeping routing areas physically small is losing effectiveness.
In yet another conventional approach, multiple rings at one or more nodes are connected in a chain/mesh configuration, which rapidly increases the number of nodes in a routing area. However, conventional methods of controlling routing area size are inadequate to sustain management of routing area requirements.
Thus, there exists a need for an improved system and an improved method for synchronous optical network (SONET) network service access point (NSAP) addressing. Such an improved system and an improved method may address some or all of the problems and deficiencies of conventional approaches identified above, and provide additional features and advantages as discussed below.